This application is in response to NOT-OD-09-058: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications. A major component of drug abuse research involves identifying the social and environmental variables that contribute to an individual's likelihood of developing problems with substance abuse and dependence. In the parent grant to this application (2R15DA014255), we proposed a series of studies examining the effects of social and environmental enrichment on measures of drug selfadministration. Those studies are nearing completion, and here we report that social and environmental enrichment during adolescence decreases responding maintained by a low dose of cocaine in female rats. One problem facing animal models of drug self-administration, especially those examining social and environmental manipulations, is that subjects must be removed from the home environment during testing. Consequently, the immediate effects of social contact cannot be examined on measures of drug self-administration that employ intravenous drug delivery. This represents a significant limitation of animal models, as drug use in humans typically occurs in the presence of others, and the behavior of these other people (i.e., whether or not they are also using drugs) can feedback to influence the drug consumption of the individual. With a few simple modifications to our existing operant conditioning chambers, we can construct a large selfadministration chamber that can also serve as a home cage for two rats. Using this chamber, we can examine drug self-administration in individual rats under conditions in which another rat is continuously present during drug self-administration sessions. Importantly, this arrangement allows us to compare drug self-administration in an animal that has a companion that also has free access to drugs (i.e., a co-user) versus an animal that has a companion without access to drugs (i.e., an abstainer). The primary aim of this project is to examine cocaine self-administration in isolated and socially housed rats, with the important caveat that the socially housed subjects will be living together in the same cage 24 hr/day, including during daily self-administration sessions. As a novel manipulation, we will examine the effects of having a companion that self-administers cocaine versus having a companion that does not self-administer cocaine. A final aim of this project is to examine these manipulations in both male and female rats to determine whether there are sex differences in the effects of social contact on measures of drug self-administration. PUBLIC HEALTH RELEVANCE: Adolescence marks a critical period in development in which individuals are particularly vulnerable to developing problems with substance abuse and dependence. Using an animal model, we will examine the effects of social contact with a companion with access to drugs (i.e., a co-user) versus without access to drugs (i.e., an abstainer) on cocaine self-administration in adolescent rats. We will examine these effects in both males and females to determine whether there are sex differences in the effects of social contact on drug-seeking behavior.